Method for separating sand from a hydrocarbon stream

ABSTRACT

An apparatus and method for separating a natural gas production stream from hydrocarbon well operations into a gas component and a sand and liquid component is described. More specifically, a sand separator comprising a cylindrical body, a production stream inlet port, a gas outlet port and a solid and liquid drain port is described. The cylindrical body has an inner cavity with an inner cone having one-way gas vents and a stationary auger wrapped around the inner cone. The production stream inlet port includes a pipe having a curved tip that directs the production stream into the body and around the inner cone and stationary auger, causing the production stream to slow down and the components to separate.

FIELD OF THE INVENTION

The invention relates to an apparatus for separating sand from a naturalgas production stream during hydrocarbon well operations. Morespecifically, the invention relates to a sand separator having aninterior space comprising an inner cone with one-way gas vents, whereinwhen a production stream enters the interior space, the sand and liquidparticles are separated from the gaseous particles.

BACKGROUND OF THE INVENTION

As is well known and by way of background, natural gas is a naturallyoccurring hydrocarbon gas mixture consisting primarily of methane, up to20% other hydrocarbons as well as varying amounts of impurities such ascarbon dioxide. Natural gas is widely used as an energy source and it isgenerally found in deep underground natural rock formations orassociated with other hydrocarbon reservoirs. The underground rockformations or subsurface reservoirs of hydrocarbons typically consist ofa porous layer, such as limestone and sand, overlaid by a nonporouslayer. The porous layer forms a reservoir in which hydrocarbons are ableto collect. To recover hydrocarbons, wells are drilled from the surfaceof the earth through the nonporous layers overlying the reservoir to tapinto the reservoir and allow the hydrocarbons to flow from the porousformation into the well. The hydrocarbons, including oil and naturalgas, are then recovered at the earth's surface where they undergofurther processing.

Recovering natural gas is often not as straightforward as it appears, asthe gas may not readily flow from the reservoir into the well bore as aresult of a variety of factors including formation characteristics andpressures. As such, as is well known in order to increase gas flow andrecovery, many methods are employed as means of increasing natural gasproduction including horizontal drilling and hydraulic fracturing, or“fracing”. Horizontal drilling, as opposed to vertical drilling,involves drilling a well more or less horizontally through a reservoirto increase the exposure of the formation to the wellbore, therebydecreasing the distance the gas must travel to the wellbore.

Hydraulic fracturing involves pumping high pressure fluids and sand intothe reservoir in order to open up the formation by fracturing the rockin the reservoir. After the pressure is released, the sand remains inthe fracture to create a higher permeability flow path towards the well.

Horizontal drilling and hydraulic fracturing are generally effective atincreasing the recovery of hydrocarbons, however they also createadditional challenges that must be dealt with. Specifically, largequantities of fluid, sand and other additives are introduced into theformation and mixed with the hydrocarbons during fracturing. After thefracing stimulation of the well, introduced fracing sand and naturallyoccurring reservoir fines or sand and/or fracing sands can be producedback into the horizontal well along with any remaining fluids, naturalgas and other reservoir fluids. This particulate is produced to thesurface and can cause plugging and/or erosion of surface equipment andpipelines.

To remove sand from natural gas at the surface, apparatuses commonlyreferred to as sand separators are used. Typically a sand separatorcomprises a vessel with an inlet port and a gas outlet port on the upperpart of the vessel, and a drain at the bottom of the vessel. Inaddition, this vessel may or may not include secondary filters. Theinside of the vessel is formatted such that when a high pressure, highvelocity production stream from a well flows into the vessel through theinlet port, it experiences a large drop in velocity, causing the naturalgas to separate from the water and sand. The vertical divider forces thefluid and sand down towards the drain, while the gas rises back uparound the divider and exits through the gas outlet port.

While past sand separators can be effective, they are often limited by anumber of operational limitations in the field. For example, the flowrate of gas and water/sand into a sand separator may be varied where thevelocity of gas and the volume of water/sand may fluctuate significantlyas it enters the sand separator. In particular, in the event that asudden pulse in water/sand is encountered, in past designs, this maylead to either ineffective water/sand separation from the gas, cloggingof the sand filters of the separator and/or damage to the sand filters.An example of a past sand separator is described in U.S. Pat. No.7,785,400. As a result, there has been a need for systems thateffectively allow for a greater residence time of water/sand within theseparator that enables a more efficient separation of water/sand fromgas without leading to clogging problems.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a separator forseparating solid and liquid components from gas components in ahydrocarbon production stream, the separator comprising: a cylindricalbody having an upper end, a lower end, a body wall and an inner cavity;an inlet pipe having a first and second end and extending through thebody wall, wherein the first end is on the outside of the body and thesecond end extends to within the inner cavity; a gas outlet port on theupper end of the body; a drain near the lower end of the body; and aninner vessel fastened in the inner cavity of the body, the inner vesselhaving a vessel wall, a vessel cavity, and a plurality of openings inthe vessel wall wherein solid and liquid components of a hydrocarbonproduction stream entering the cylindrical body are preferentiallydirected to the drain and gas components are preferentially directed tothe gas outlet port.

In a further embodiment, the inner vessel is cone-shaped having a widerupper end in relation to a narrower lower end.

In one embodiment, each of the plurality of openings in the vessel wallincludes one-way gas vents. Each gas vent may include a cap partiallycovering each opening.

In another embodiment, the separator includes a stationary augeroperatively connected to an inner surface of the body wall andoperatively positioned between the inner vessel and the inner surface ofthe body wall. Preferably, the auger is separated from the inner vesselby a gap and/or has an inwardly and downwardly sloping surface.

In another embodiment, the separator includes a wear plate fastened tothe body wall in the inner cavity adjacent the second end of the inletpipe.

In yet another embodiment, the inner vessel further comprises at leastone inwardly projecting ledge extending around the vessel wall withinthe vessel cavity.

In another aspect, the invention, provides a method for separating solidand liquid components from gas components in a hydrocarbon productionstream comprising the steps: a) transporting the production stream intoa cylindrical vessel; b) creating an initial drop in velocity of theproduction stream; c) directing the production stream flow around aninner cavity of the cylindrical vessel; d) collecting the gas componentsfrom the production stream at a top end of the vessel; and e) collectingthe sand and liquid components at a bottom end of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to the accompanying figures inwhich:

FIG. 1 is a front perspective cutaway view of a sand separator inaccordance with one embodiment of the invention;

FIG. 2 is a front cutaway view of a sand separator in accordance withone embodiment of the invention;

FIG. 3 is a front view of a sand separator in accordance with oneembodiment of the invention; and

FIG. 4 is a top cross-sectional view of the sand separator taken at line‘4-4’ of FIG. 2 in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the figures, a sand separator 10 is described. Thesand separator generally comprises a vessel 12 having an inlet pipe 20,a gas outlet pipe 30 and a drain 40. The interior of the sand separatorcomprises a collecting plate 46, an inner cone 50, a wear plate 60, andan auger 70. The sand separator is described herein with typicaldimensions and as being manufactured from specific materials. It isunderstood, however, that variations in the dimensions and materials maybe made while achieving the objectives of the invention as understood bythose skilled in the art.

Vessel

Referring to FIGS. 1 and 2, the vessel 12 is preferably a cylindricalshaped hollow vessel having an outer wall 12 a, inner cavity 12 b, topend 12 c, bottom end 12 d. The external dimensions of the vessel aretypically about 3 to 6 feet in diameter and 6 to 10 feet in height. Theouter wall 12 a, top end 12 c and bottom end 12 d of the vessel arefabricated from rolled steel and are of sufficient thickness toaccommodate an internal pressure of up to 5000 psi. The top end 12 c ofthe vessel has a flange 14 with a plurality of bolt holes 14 a forattachment to a pipe or other device. The bottom end 12 d of the vesselis secured to a stand or legs for support (not shown).

The vessel 12 comprises three ports from the outside of the sandseparator to the inner cavity 12 b: the inlet pipe 20 located in the tophalf of the outer wall 12 a; the gas outlet pipe 30 located on the topend 12 c of the vessel; and the drain 40 located on the bottom end 12 dof the vessel. Each pipe port is moveable between an open and closedposition and has a flange 20 a, 30 a, and 40 a for fastening tocomplimentary pipes, hoses or other conveyance devices.

Inner Cone

Referring to FIGS. 2, 3 and 4, the inner cone 50 is located in the innercavity 12 b of the vessel and comprises an upper end 50 a, a lower end50 b, a cone wall 50 c and a cone cavity 50 d. The upper end 50 a of thecone is connected to an inner surface 12 e of the top end 12 c of thevessel. There is a continuous path between the cone cavity 50 d and thegas outlet pipe 30. The lower end 50 b of the cone has an opening 50 fto allow sand and liquid to drain from the cone cavity.

The cone wall 50 c includes a plurality of reverse entry gas vents 52that allow gases to flow into the cone cavity 50 d while obstructing theflow of particulates from entering the cone cavity 50 d. The gas vents52 preferably include a cap 52 a covering each vent opening such that achange in direction is required for gas/solid/liquid to flow througheach gas vent opening. In addition, each cap is preferably positioned indownwardly angled parallel rows in line with the angle of the inlet pipe20.

On an inner surface 50 g of the cone wall 50 c, there is a first andsecond circular ledge 54 a, 54 b that protrudes inwardly from the innersurface of the cone wall and extends around the inner circumference ofthe cone wall slightly above a row of gas vents.

Collecting Plate

Referring to FIGS. 1 and 2, the collecting plate 46 is located near thebottom end of the interior of the vessel 12, spanning across the innercavity to collect the sand particles and liquids that drop out of theproduction stream and direct them towards a channel 46 a in the middleof the collecting plate. The channel connects to the drain 40 to allowthe collected stream to flow out the vessel.

Inlet Pipe

Referring to FIG. 4, the inlet pipe 20 comprises a first opening 62, abody 64 having a curved tip 66 and a second opening 68. A wear plate 60is fastened to the inner surface of the vessel near the curved tip 66 ofthe inlet pipe. The pipe body 64 is preferably positioned at a slightdownward angle of approximately 10 degrees to the horizontal.

The body 64 of the inlet pipe is preferably made of a hard metal towithstand high levels of abrasion from the production stream 80colliding with the inner walls of the body. The wear plate 60 protectsthe vessel wall from abrasion due to high-pressure high-speed particleshitting it continuously during use. When the wear plate is abraded to acertain extent, it can be removed and replaced quickly, thereby savingthe whole vessel from being replaced and thereby saving time, money andlabor.

Auger

Referring to FIGS. 1 and 2, the auger 70 is located around the innercone 50 in the inner cavity 12 b of the vessel 12. The auger 70 isstationary and comprises a surface 72 attached to the inner surface 12 eof the vessel that spirals around the inner cone 50 and getsprogressively wider from top to bottom, with a gap 74 located betweenthe auger and inner cone.

Operation

As shown in FIG. 4, the production stream comprising gases 82 (dottedline), sand and other particulate matter 84, and liquids 86 (solidline), enters the vessel through the first opening 62 of the inlet pipe20. The production stream enters the vessel with highly variablevelocities that are determined by the gas production volumes andpressures, shown as V₀ in FIG. 4. The production stream flows throughthe body 64 of the pipe, around the curved tip 66 of the inlet, out thesecond opening 68, and collides with the wear plate 60. As theproduction stream exits the second opening, the volume available for theproduction stream is greatly expanded from the unit volume of the inletpipe, thereby causing a large initial drop in the velocity of theproduction stream (designated as V₁). For example, high pressure fluidsin a typical 2 inch diameter inlet pipe may enter the vessel at alocation having a nominal 21 inch diameter which thereby results in anapproximate 110 fold change in cross-sectional area at the point oftransition which similarly results in a 110 fold change in flow velocityof the production stream.

Upon exiting the second opening and after impacting the wear plate,initially the lighter gas fractions due to their lower density and lowercentrifugal forces acting on the lighter fractions will flow towards thegas vents 52. The heaver particles of sand and liquid, shown by thesolid arrows, and the heavier gas fractions will be propelled around theinner walls of the vessel, where they continue to slow to velocities V₂and V₃. Moreover, these fractions will also spiral downwards towards thebottom of the vessel due to impacting with the auger. The downwardspiral direction is initiated by the downward angle and curved tip ofthe inlet pipe. Continued contact with the auger 70 continues to slowand direct the stream downwards as the stream spirals around the ledge72 of the auger thus reducing the centrifugal forces on the gas/liquidfractions. The lower centrifugal forces on the gas fractions willcontinue to enable the gas fraction to enter the cone through gas vents52 while the slowing liquids and solids will drop from suspension.Importantly, the gap 74 between the auger ledge and the inner cone aswell as the inward slope of the auger prevents droplets/particles fromcollecting and/or stalling on the auger ledge and allows them to falldownwards towards the collector plate 46. The auger also minimizes theformation of a vortex in the vessel that might otherwise form if thevelocity of gas/liquids is not slowed gradually.

When the gases flow through the gas vents 52 into the cone cavity 50 d,depending on the relative velocities, some sand 84 and liquid 86particles may not drop out of the production stream 80 and will flowwith the gas through the gas vents. When the gas, sand and liquid streamflows through the gas vents, the stream will initially collide with theunderside of the first and second ledge 54 a, 54 b, thereby creating alow velocity zone that causes substantially all of the carried-over sandand liquid particles to drop out of the gas stream and thereby fall downthe cone where they drop or flow out of the opening 50 f in the bottomof the cone onto the collecting plate 46. In contrast, the gas streamreadily flows around the first and second ledge 54 a, 54 b, to exit thegas outlet pipe 30 at the top end of the vessel 12.

When the solid/liquid phases reach the bottom of the auger or the coneopening 50 f, they fall onto the collecting plate 46, flowing throughthe channel 46 a and out the drain 40. Typically large sand particlesgreater than 50 μm in diameter and most of the liquids are collected.The drain may be connected to a settlement tank wherein the sand andliquid particles are further separated for disposal.

Most of the gases from the production stream exit the vessel through thegas outlet pipe 30 and may be subjected to further separationtechniques, such as a filtering device, downstream from the sandseparator in order to remove any finer particulate matter.

The sand separator as described typically separates approximately 91% ofthe particulate matter (i.e. sand) from the production stream. Theremaining particulate matter is typically smaller sand particles of lessthan 50 μm that can be, if required, filtered out downstream. Anyremaining smaller particulate are less able to either plug or erodesurface equipment.

System Advantages

The sand separator as described is able to effectively separate gas fromproduction streams, especially high pressure, high velocity productionstreams that also comprise liquid and particulate phases. The gascomponent is mostly natural gas, whereas the liquid and particulatephases are primarily water and sand; however other solid/liquids mayalso be present. Production streams from the early stages of horizontalwell fracturing can have initial pressures from 3000 to 5000 psi, and attimes up to 10,000 psi. As such, the flow rates through typical 3 to 4inch production lines can approach a million cubic feet per hour ormore, resulting in extremely high velocities entering the vessel.

Importantly, the subject system has several advantages over conventionalsand separators by providing effective surfaces to slow each of the gas,liquid and solid phases entering the system. As such, a more effectiveseparation can be achieved with less solid/liquid carryover. That is,the subject design allows for a more controlled release of sand from thefast moving gas as the auger will more gradually decrease the velocityof the liquid/sand entering the separator such that the flow rate ofseparated liquid/sand is more consistent to the outlet. This isimportant in addressing sudden changes in flow rates of liquid/sand thatmay be encountered by the device.

In addition, the replaceable removable insert reduces the abrasioncaused to the vessel from the particulate matter entering the vessel athigh speeds, thereby prolonging the life of the vessel. Also, theremovable insert is relatively inexpensive and easy to change, requiringonly minimal labor and tools, and replacement can be performed on-siteas needed without having to transport the sand separator.

Although the present invention has been described and illustrated withrespect to preferred embodiments and preferred uses thereof, it is notto be so limited since modifications and changes can be made thereinwhich are within the full, intended scope of the invention as understoodby those skilled in the art.

1-15. (canceled)
 16. A method for separating solid and liquid componentsfrom gas components in a hydrocarbon production stream, the methodcomprising the steps of: a) conveying the production stream into acylindrical vessel having an inner cavity; b) creating an initial dropin velocity of the production stream; c) directing the production streamto flow around the inner cavity; d) collecting the gas components fromthe production stream at a top end of the vessel; and e) collecting thesolid and liquid components at a drain in a bottom end of the vessel.17. The method of claim 16, wherein the inner cavity comprises acone-shaped inner vessel with a downwardly directed apex.
 18. The methodof claim 17, wherein the inner vessel comprises a plurality of openings,including one or more gas vent openings.
 19. The method of claim 17,wherein the flow around the inner cavity is a downward spiral flow. 20.The method of claim 19, wherein the downward spiral flow is induced by astationary auger operatively connected to an inner sidewall of the innercavity.
 21. The method of claim 20, wherein the auger is positionedbetween the inner vessel and the inner sidewall of the inner cavity. 22.The method of claim 21, wherein the auger is separated from the innervessel by a gap.
 23. The method of claim 22, wherein the auger has aninwardly and downwardly sloping surface.
 24. The method of claim 23,wherein the production stream is conveyed into the cylindrical vesselvia an inlet pipe opening into the cylindrical vessel, and a wear plateis fastened to the inner sidewall in the inner cavity adjacent theopening into the cylindrical vessel.
 25. The method of claim 24, whereinthe wear plate is removable.
 26. The method of claim 16, wherein acollecting plate is located above the drain, the collecting plate havinga channel in fluid communication with the drain.
 27. The method of claim20 wherein the inner vessel further comprises at least one inwardlyprojecting ledge extending around the inner sidewall.
 28. The method ofclaim 24, wherein the inlet pipe is angled downwards.
 29. The method ofclaim 24, wherein the inlet pipe opening is curved inwardly.
 30. Amethod for separating solid and liquid components from gas components ina hydrocarbon production stream, the method comprising the steps of: f)conveying the production stream into a cylindrical vessel having aninner cavity; g) creating an initial drop in velocity of the productionstream by inducing a downward spiral flow of the production stream; h)collecting the gas components from the production stream at a top end ofthe vessel; and i) collecting the solid and liquid components at a drainin a bottom end of the vessel.
 31. The method of claim 30, wherein theinner cavity comprises a cone-shaped inner vessel with a downwardlydirected apex.
 32. The method of claim 31, wherein the inner vesselcomprises a plurality of openings, including one or more gas ventopenings.
 33. The method of claim 30, wherein the downward spiral flowis induced by a stationary auger connected to an inner sidewall of theinner cavity.
 34. The method of claim 33, wherein the auger has aninwardly and downwardly sloping surface and is positioned between theinner vessel and the inner sidewall of the inner cavity.
 35. The methodof claim 33, wherein the production stream is conveyed into thecylindrical vessel via a downward angled inlet pipe with an inwardlycurved opening into the cylindrical vessel, and a wear plate is fastenedto the inner sidewall in the inner cavity adjacent the opening into thecylindrical vessel.